Great post Ruth, clear and understandable in a systematic way written. I'm also on the verge of changing domains, but I'm still indecisive if I would go for the surprise switch in 1 day from Old to New site- like SEOmoz.org to Moz.com - or for the switch in which both sites will be live simultaneously with a canonical from Old to New site.

Beside the surprise affect why would you go in one GO and not go for simultaneously?
Or conflicts in Keywords ranking?